1. Field of the Invention
The present invention relates to a new process for the production of optionally cellular moldings which have an impervious skin, and an improved surface quality.
2. Description of the Prior Art
The production of moldings which have an impervious skin and a cellular core according to the isocyanate-polyaddition process is known in principle (c.f. Kunststoffe 60, pages 3-7 (1970) or DE-AS No. 1,196,864). It is possible to produce elastomeric and also rigid moldings by this process by an appropriate choice of starting materials. If no blowing agents or only small quantities thereof are used in the process, solid moldings are produced. The raw materials are preferably processed according to the so-called reaction injection molding process (RSG or RIM process). This is a filling technique by which liquid starting materials are introduced into closed molds via so-called automatically controlled mixing heads over the shortest time possible. In the production of moldings for the automobile industry, di- and/or tri-functional polyether polyols having for example a molecular weight ranging from 3000 to 7000 and low molecular weight diols such as ethylene glycol and/or butane diol-1,4 or aromatic diamines having sterically hindered amino groups are reacted with polyisocyanates, preferably liquid polyisocyanates or polyisocyanate mixtures of the diphenylmethane series, optionally in the presence of blowing agents (c.f. U.S. Pat. No. 4,218,543 or U.S. Pat. No. 4,065,410). The moldings which are produced in this manner have excellent mechanical properties. It has been found that the moldings occasionally have surfaces which are not completely free of cavities and pores. Surface defects of this type may become visible by rubbing the molding with a colored powder and may be recognized by a brightening, light-scattering effect in contrast to a deep black (inking with graphite) undisturbed surface.
Surface defects of this type in the form of pores or scars, so-called "pin-holes," often have to be primed with a repairing or filling composition and subsequently sanded and polished, possibly degreased prior and subsequent to this, and optionally lacquered, thereby requiring great expenditure for their removal.
Accordingly, it is an object of the present invention to provide a process for the production of polyurethane moldings which do not have surface defects of this type.
This object was achieved by the process according to the present invention which will be described in more detail in the following.